As discussed: https://gcc.gnu.org/ml/gcc-patches/2014-10/msg00420.html

2014-10-15  Joern Rennecke  <joern.rennecke@embecosm.com>
            Jeff Law  <law@redhat.com>

        * caller-save.c (replace_reg_with_saved_mem): If saved_mode covers
        multiple hard registers, use smaller mode derived from MODE.

Co-Authored-By: Jeff Law <law@redhat.com>

From-SVN: r216243

gcc/ChangeLog

+2014-10-15  Joern Rennecke  <joern.rennecke@embecosm.com>
+	    Jeff Law  <law@redhat.com>
+
+	* caller-save.c (replace_reg_with_saved_mem): If saved_mode covers
+	multiple hard registers, use smaller mode derived from MODE.
+
 2014-10-15  Andreas Schwab  <schwab@suse.de>
 
 	* explow.c (convert_memory_address_addr_space_1): Mark in_const

gcc/caller-save.c

@@ -1158,9 +1158,12 @@ replace_reg_with_saved_mem (rtx *loc,
 	  }
 	else
 	  {
-	    gcc_assert (save_mode[regno] != VOIDmode);
-	    XVECEXP (mem, 0, i) = gen_rtx_REG (save_mode [regno],
-					       regno + i);
+	    enum machine_mode smode = save_mode[regno];
+	    gcc_assert (smode != VOIDmode);
+	    if (hard_regno_nregs [regno][smode] > 1)
+	      smode = mode_for_size (GET_MODE_SIZE (mode) / nregs,
+				     GET_MODE_CLASS (mode), 0);
+	    XVECEXP (mem, 0, i) = gen_rtx_REG (smode, regno + i);
 	  }
     }